1. Field of the Invention
This invention relates generally to a network architecture providing improved utilization communication information between digital subscriber lines and communications devices, and more particularly to increasing performance of router systems for transferring digital communications information between various different types and numbers of modem through digital subscriber lines.
2. Description of the Prior Art
Routers are employed in the telecommunications area as sophisticated switches. That is, a router is a device that can select a path data should take thereby requiring the router to have an understanding of the network and how to determine the best route for the data path.
Servers are sophisticated storage devices that maintain information, such as web pages, for access by various other communications equipment such as PCs. Information between servers, PCs and the like, may be transferred through routers.
Information that is transferred by routers between various communications equipment is often times in the form of packets and coupled onto communication links (or lines) using Time Division Multiplexing (TDM). This is perhaps best understood by describing an example commonly employed by users.
When data such as electronic mail is transmitted over the internet, the data is diced up into small packages called packets, each packet having an address attached. The packets flow through the circuits of the internet, such as routers, servers and so forth, but they do not all necessarily follow exactly the same path. They do however, all arrive at the same destination, and are reassembled into the original data. The various packets belonging to the same original data are identified by the use of their attached address.
Devices that send data through routers do so at various times on various communications channels that serve as links for transferring the data from the devices, through the routers, and to the final device destination. The path from a device to a router includes such communications links or TDM streams. Data through such streams is transferred for each device when the link is not busy and given a time slot during which the data belonging to a particular device is coupled onto the link and transferred. A link may carry information from various devices to the router, accordingly, data from various devices are multiplexed.
With the advent of recent advancements in router technology, there has been an important requirement placed on routers. The requirement calls for the universal support of various xe2x80x98featurexe2x80x99 boards that have been developed recently to support a variety of modem and other communications devices. Feature boards are complex printed circuit boards that may serve various purposes. For example, a xe2x80x98trunkxe2x80x99 feature board within a router may serve to receive digital information from multiple TDM streams onto which the digital information is coupled. The trunk feature board may be electronically coupled, through a TDM backplane, to various xe2x80x98modemxe2x80x99 feature boards. These modem feature boards transfer information from the trunk feature card to many modems of various types. This is perhaps best described by the use of a diagram.
FIG. 1 depicts a router 10 coupled to a central office 12, which may be a telephone company switch, through a set of communication links 14 that may be of T1 or E1 industry standard form of communication line. T1 and E1 comply with standards set by the Institute of Electrical and Electronics Engineering (IEEE) for multiplexing various communication information from various sources (or devices) for transmission to other devices. The communication lines, individually, are commonly referred to as Digital Subscriber 0 (DS0).
Router 10 includes a trunk feature card 16 coupled through a TDM backplane 18 to a modem feature card 20. While not shown in FIG. 1, a router may include more than one modem feature card. The modem card 20 couples modem signals for transfer thereof to modem devices. Rather than modem signals and devices, Digital Signal Processing (DSP) signals and devices may be similarly employed.
The TDM backplane 18 transfers TDM streams and channels from the trunk card 16 to the modem card 20 by coupling the same onto a first plurality of TDM streams 22 (for coupling signals from the trunk card 16 to the backplane 18) and a second plurality of TDM streams 24 (for coupling signals from the backplane 18 to the modem card 20).
The trunk card 16 and the modem card 20 each include a first TDM chip 26 and a second TDM chip 28, respectively. These TDM chips are integrated circuits for arranging information, that is sent through the TDM communications link, into frames and vice versa. Each frame includes a predetermined number of channels and each channel carries information for a specific device that is using the router 10 for transferring information to another device. In a system that uses T1 communication links, there are 24 channels in a frame and in a system that uses E1 communication links, there are 30 channels in a frame.
Cisco Systems, Inc. designs, develops and manufactures various types of router products commonly employed in the industry for transferring internet information, arranged in packets, and for other types of telecommunications applications. One such router is referred to as the AS5200 and another is the AS5300 family of products.
Whereas the AS5200 supports 4 TDM streams carrying TDM information through a TDM backplane, the AS5300 supports 8 TDM streams. As described above, the modem feature cards(s) rely on the TDM backplane, which receives TDM streams, to communicate with external equipment through the trunk feature card.
One of the problems that arises with respect to prior art router systems, such as the one shown in FIG. 1, is that access to TDM streams is limited to four streams. While in routers supporting fewer number of modems (such as 60 modems), this was acceptable, a problem arises in recently-developed routers, which may support 240 or more modems. Each TDM stream can typically transfer 30 modem channels (using E1) and since previous router designs only had four TDM stream interfaces that were dedicated (not dynamically allocatable) lines, if trunk cards having more than 120 DS0 line interfaces were used, only 120 modem channels could be supported before having to share a channel by various modems. For example, if the modem feature cards supported 180 modems, due to the streams being limited in number to four, and with each stream carrying 30 channels, 60 of the modem channels would not be usable thereby introducing an over-subscription problem to the system. This is because TDM channels cannot be shared.
Dedicated TDM stream lines only allow for statically-allocated TDM time slots assigned based upon the order in which the feature boards in the router system are identified when the system is first powered-on. Moreover, each modem in the system only has one dedicated TDM backplane time slot. Once these backplane timeslots are allocated, the relationship between the time slots and the modems stays unchanged throughout the lifetime of the router until the next initialization of the system, after which this relationship again becomes fixed.
Another problem that arises with the advent of recently-developed router technology is the capability of using old trunk and modem feature boards in combination with more recently-designed trunk and modem feature boards such that the old boards and the new boards inter-operate with each other seamlessly.
The trunk feature cards may be considered xe2x80x98Producersxe2x80x99 of TDM backplane stream resources (or time slots) and the modem feature cards may be considered xe2x80x98Consumersxe2x80x99 of the TDM backplane stream resources in that they consume or utilize time slots for effecting communication of modem or telecommunications signals between modem devices and other devices.
When a router system includes a mixed combination (xe2x80x98oldxe2x80x99 and xe2x80x98newxe2x80x99 versions) of trunk and modem feature cards, the TDM resources that are produced by the trunk feature cards may not be accessible by the modem feature cards because new trunk feature cards may be in use with old modem feature cards that may not support additional TDM resources. Similarly, new modem feature cards, when in use with old trunk cards, may attempt to request resources that can not be produced by old trunk feature cards.
In prior art techniques, to resolve this problem and have all of the feature cards inter-operate with each other, the driver-level software program was designed to maintain knowledge of which feature cards are installed in the router system so that the resources produced (time slots allocated) may all be employed by the Consumer. However, the problem with this approach is that feature boards have their own physical limitation in that they have access to a set group of wiring without the capability to share these resources outside of what has been assigned to them. For example, a feature board may only have access to a first group of wiring without the capability of sharing any other groups of wiring, which would limit access by that feature board to a predetermined number of digital subscribers. Where, for example, more modems are in the system than the number of digital subscribers, some modems would not be utilized resulting in an under-utilization of the resources available in the system.
Yet another problem associated with prior art techniques is known as xe2x80x9cover-subscriptionxe2x80x9d, which occurs when the number of modem devices (and therefore channels) exceeds the number of Digital Subscriber (DS0) channels that may be supported by a trunk card. This is because each type of modem card can support a predetermined number of modems, i.e. a modem card can support up to a predetermined number of (or less but not more) modems, and each type of trunk card similarly can only interface with a predetermined number of TDM streams.
With the static allocation of the backplane timeslots in an over-subscribed system, some of the modems would never be accessible since there is just not enough backplane timeslot resources for all of the modems to support either incoming or outgoing calls.
For example, what is referred to by Cisco Systems, Inc. as their xe2x80x98Quadxe2x80x99 type of trunk card can support 4 TDM streams, which provides T1 or E1 connections of up to 120 DS0s for use by either digital or analog circuits. In router systems of prior art technology, there can be no more than 120 modems that would exist in the same system utilizing the Quad trunk card. This would allow each modem to be connected to one DS0 causes, in total, up to 120 DS0-to-modem connections. However, with the introduction of new modem feature boards (such as Amazon II family of Cisco Systems products), the number of modems can go from 120 to 240 when there are two such modem feature boards installed in the router system. This creates an xe2x80x9cover-subscriptionxe2x80x9d problem due to the number of modems exceeding the number of available DS0S.
Therefore, the need arises in a router system to provide the capability of employing feature cards that can be installed in any order. A method is required for allowing flexible electrical coupling of various feature boards such that the software program employed by each of the feature boards (or cards) would allow producing or consuming of the TDM backplane stream resources without apriori knowledge of the characteristics of the TDM backplane as well as the various different feature boards that are installed in the router system.
Furthermore, with the need for providing universal support of old and new feature boards, there further arises the need for the router system to provide connectivity for all of the possible feature boards that can co-exist in the same router system.
What is further needed is a router system that allows inter-operability of various different combinations of modem cards and trunk cards, effectuating flexible and dynamic allocation of modems to TDM streams for maximizing the utilization of communication links to increase the overall performance of router systems. Additionally, the capacity of subscribers (using DS0lines) can be extended as new modem boards are upgraded.
Finally, a router system is needed to support the mixture of various types of feature boards for dynamically managing the backplane timeslots resources.
Briefly, a digital communications system for coupling a plurality of digital communication devices to a central office includes a backplane; a trunk card device coupled to Digital Subscriber (DS) channels and further coupled to a first trunk group of streams and a second trunk group of streams, the first and second trunk streams for transferring modem information to and from the DS channels through the backplane; and at least one modem card device, coupled through a first modem group of streams and a second modem group of streams to said backplane, for transferring modem information through the backplane to the DS channels. Each modem card controls a predetermined number of modem units to transfer modem information between the modem units and the DS channels through the backplane, wherein the first and second modem group of streams are selectably assignable to transfer information, through the backplane, to the first and second trunk group of streams such that each modem unit is assigned a communication channel for transferring modem information thereby allowing full utilization of all of the modem units.
The foregoing and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments, which make reference to the several figures of the drawing.